1. Field of the Invention
The present invention relates to a feedback compensating apparatus adapted to adjust the working condition of a working machine for a workpiece to be processed next, by feeding back dimensional error data associated with already processed workpieces.
2. Discussion of the Related Art
A feedback compensating apparatus as described above is used for a working system including (a) a working machine for performing successive working operations on a plurality of workpieces, (b) machine control means for determining a working condition of the working machine on the basis of an extraneous compensating signal and controlling the working machine according to the determined working condition, and (c) a measuring device for measuring actual dimensions of the workpieces processed by the working machine. The feedback compensating apparatus is constructed so as to include (i) determining means for determining a compensating value as said extraneous compensating signal for the workpiece to be processed next, on the basis of the actual dimensions of the already processed workpieces which have been measured by the measuring device, and (ii) applying means for applying the determined compensating value to the machine control means.
In some working systems, the measuring device is adapted to measure the workpieces immediately after the workpieces are processed by the working machine. In this case, the workpiece processed under the working condition influenced by the currently effective or last compensating value is measured shortly after the working operation on that workpiece is completed. Therefore, an influence of the last compensating value appears on the last measured workpiece, and the measured dimensions of the recently processed workpieces can be used to check the last compensating value for adequacy, immediately after the last compensating value is used. Where the above-indicated feedback compensating apparatus is used for this type of working systems, it is comparatively easy to improve the accuracy of determination of the compensating values for adjusting the working condition of the working machine.
In another type of working systems, however, there exist pre-measured workpieces between the working machine and the measuring device. The pre-measured workpieces are the workpieces which have been processed by the working machine but have not been measured yet by the measuring device. These pre-measured workpieces cause a so-called "dead time", which is a time required for the first workpiece influenced by the currently effective or last compensating value to be measured by the measuring device. In other words, an influence of the last compensating value appears on the actually measured dimension after the dead time has passed after the workpiece is processed under the influence of that compensating value. For this reason, it is comparatively difficult to determine the compensating values with high accuracy, where the feedback compensating apparatus is used for the working systems of this second type in which the dead time exists.
In view of the second type of working systems, the assignees of the present application have made a research to develop an improved feedback compensating apparatus capable of dealing with the "dead time" or the existence of "pre-measured workpieces", and proposed the apparatus including (a) improved determining means for determining the present compensating value and (b) applying means for applying each determined compensating value to the machine control means for adjusting the working condition of the workpieces to be processed next. This improved determining means is adapted to store in suitable memory means dimensional values of the processed workpieces measured by the measuring device, and update the compensating value, namely, determine each present compensating value for adjusting the working condition of the workpieces to be processed next. This determination of each compensating value is made on the basis of a predetermined number of the last stored dimensional values of the workpieces which have been processed under the same working condition determined or influenced by the currently effective or last compensating value. After the present compensating value is determined at the end of each automatic compensating interval or cycle, an estimated dimensional value is obtained when each processed workpiece is measured in the next automatic compensating cycle, until the measuring device completes the measurement of the workpiece which immediately precedes the first workpiece processed under the working condition influenced by the last compensating value which precedes the compensating value to be determined next. Each estimated dimensional value is obtained on the basis of the measured dimensional value of the corresponding workpiece and the last compensating value, assuming that the workpiece whose dimension is measured was processed under the working condition influenced by the last compensating value, while the working condition for that workpiece was not in fact influenced by the last compensating value. The thus obtained estimated dimensional values are stored in the memory means, and the compensating value is updated on the basis of the stored estimated dimensional values when the number of these stored estimated values reaches a predetermined value.
The determining means indicated above is based on an assumption that the first workpiece influenced by the last determined and currently effective compensating value is measured by the measuring device at a given point of time during each automatic compensating interval or cycle which begins with the commencement of storing of the measured values and ends with the determination of the present automatic compensating value used for the workpieces to processed next. Referring to the schematic view of FIG. 38 in which each rectangular block indicates an automatic compensating interval or cycle, an influence of the last compensating value Ui-1 determined at the end of a given compensating cycle appears on the dimensional values actually measured by the measuring device at a given point of time during the next compensating cycle in which the present compensating value Ui is determined. In FIG. 38, the influences of the compensating values U are indicated by stepped drops of the actually measured value indicated by solid line. During a period from the beginning of each automatic compensating cycle to the moment at which the influence of the last compensating value Ui-1 first appears on the measured value, estimated dimensional values are obtained each by adding the last compensating value Ui-1 (currently effective value) to each actually measured value (which was not in fact influenced by the last compensating value), and the thus obtained estimated values are stored in the memory means. In the following period between the moment at which the influence of the last compensating value Ui-1 first appears on the measured value and the moment at which the present compensating value Ui is determined, the actually measured values are stored in the memory means. The present compensating value Ui is determined on the basis of a predetermined number of the stored values (which include the estimated values).
The improved feedback compensating apparatus described above does not require a manual operation of the operator of the working system when each compensating value is determined by the determining means. In some cases, however, manual compensation or adjustment of the machine working condition by the operator is desired to assure high quality of the processed workpieces. For instance, this manual adjustment is desired when the working tool (such as a grinding wheel used on a grinding machine) is replaced or changed.
Even when the working tool is changed, the automatic compensation or adjustment of the working condition of the working machine as described above permits the actual dimensions of the processed workpieces to gradually approach and finally coincide with the desired or nominal value. In a working system having the dead time or pre-measured workpieces, however, the workpieces which have been processed shortly after the new working tool is used may be unacceptable as the final product, with their dimensions being outside the tolerable range, since the compensating value to adjust the working condition of the machine cannot be updated until the workpiece first processed by the new working tool is measured by the measuring device. In the light of this drawback, it is desirable to provide a quality checking station between the working machine and the measuring device, preferably at a position as near as possible to the working machine, so that the operator of the machine may inspect the processed workpieces for the processing accuracy (quality of the product), as needed, or when there arises anything that causes a comparatively large change in the measured dimensions of the processed workpieces, for example, when the working tool is changed. The operator manipulates suitable data input means to enter an appropriate manual compensating value, which is determined on the basis of a result of the inspection of the processed workpieces at the checking station. One form of the working system provided with such checking station is schematically illustrated in FIG. 39, in which the working machine, checking station and measuring device are indicated at CK 110 and 112, respectively.
The assignees of the present application has further improved the above-indicated improved feedback compensating apparatus, so that the improved determining means is capable of effecting not only the automatic compensation as described above, but also manual compensation according to a manual compensation command entered by the machine operator. The thus improved apparatus is adapted, as indicated in the schematic view of FIG. 40, such that an automatic compensating cycle is interrupted or terminated if a manual compensation command is entered by the operator during that automatic compensating cycle, and a manual compensating value U' determined based on this command is applied to the machine control means. Then, a new automatic compensating cycle is performed. In the new automatic compensating cycle, the measured dimensional values which have been stored in the memory means during the interrupted cycle are ignored or discarded, and the currently effective manual compensating value U' is added to each newly measured dimensional value, to obtain estimated dimensional values. These estimated values are the dimensions of the workpieces which are expected to be established if the workpieces were processed under the working condition adjusted or influenced by the manual compensating value U'. The estimated values are stored in the memory means, and the present automatic compensating value Ui is determined on the basis of a predetermined number of the stored estimated dimensional values.
In the second improved feedback compensating apparatus whose operation is illustrated in FIG. 40, the influence of the previous automatic compensating value Ui-2 which is determined at the end of the automatic compensating cycle immediately preceding the interrupted cycle is not taken into account to obtain the estimated dimensional values. That is, the estimated dimensional values are determined solely on the basis of the manual compensating value U', which is the last compensating value. However, the influences of not only the manual compensating value U' but also the previous automatic compensating value Ui-2 should be taken into account, for the initial period from the beginning of the new automatic compensating cycle to the moment at which the influence of the previous automatic compensating value Ui-2 first appears on the actually measured dimension, as indicated in the schematic view of FIG. 41 wherein the new automatic compensating cycle is indicated by a complete rectangular block. That is, both of the compensating values Ui-2 and U' should have influenced the measured dimensions of the processed workpieces if the workpieces were processed under the working condition influenced by these two compensating values. Therefore, some of the estimated dimensional values determined by the manual compensating value U'only may be considerably different from the value which accurately reflect the actual current working condition which is influenced by both of the manual compensating value U' and the previous automatic compensating value Ui-2. Thus, the use of the manual compensating value U' only to obtain the estimated values does not assure accurate estimation of the actual working condition and suitable determination of the present automatic compensating value Ui for the workpieces to be processed next.
It will be understood that the second improved feedback compensating apparatus suffers from a problem that some of the estimated dimensional values obtained in an automatic compensating cycle following the generation of a manual compensation command considerably deviate from the dimension of the workpieces that should be obtained when the workpieces are processed under the actual working condition, whereby the accuracy of determination of the automatic compensating value tends to be deteriorated.
The above problem is encountered not only when the manual compensating value is entered during the automatic compensation, but also when only the manual compensation alone is effected continuously. Further, the problem is encountered also when only the automatic compensation alone is effected continuously. This may be caused because the influence of the last automatic compensating value does not necessarily appear on the measured workpiece dimensions in the present automatic compensating cycle during the continuous automatic compensation, contrary to the assumption described above. For example, the influences of two successive previous automatic compensating values Ui-2 and Ui-1 (one of which is the last compensating value) may appear in the present automatic compensating cycle.